Hey, guys; I've been playing around with pipes, o-rings, solder, the Internet, and the GGDT trying to figure out how to get maximum ft/lbs from pressurized-gas propellants. As far as I can tell, with standard pressures (800 to 2,000 PSI), the velocity is limited by the expansion speed of the gas in atmosphere. (I'm ignoring vacuum-barreled guns for practicality) In practical terms, it's also limited by the volume of pressurized gas available.

With standard pressures, it seems you have to choose between high-velocity/low-mass shooting, or low-velocity/high-mass shooting. In both cases, it's a trade off. The low-mass rounds have limited ft/lbs of force, but the high-mass rounds don't go fast enough to carry far. Of course, the high-mass rounds could be moved up to higher velocity by a greater volume of propellant...

So, mostly out of curiosity, I'm wondering what you guys' thoughts on pressures are. Assuming a machine shop, machinist's knowledge, and good materials, what kind of pressures are achievable? What's the limit of safety with pressures? And at what point does higher pressure require insanity?

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Last edited by mako on Wed Nov 18, 2015 2:05 pm, edited 1 time in total.

“Whenever you find yourself on the side of the majority, it is time to pause and reflect.”Mark Twain

Hydraulic fittings are commonly rated to 8,000-10,000 psi, that would be the "sane" limit to me - but then you're going to have to figure out how to pressurize gas to those levels - unless of course you do the sensible thing and go hybrid

It'd have to be a pretty small valve, right? At 8,000 PSI... that's what, over 1,500 pounds of force on a 0.25 inch diameter valve face? You'd need a heck of a hammer, not to mention a pretty sturdy valve stem.

Counter balanced? How do you counter balance a hammer valve?

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“Whenever you find yourself on the side of the majority, it is time to pause and reflect.”Mark Twain

As Gippeto noted it's important to have a relatively small contact area between the delrin and metal faces in order to maximize pressure and seal at lower pressures. The t-shirt launcher I posted recently has an aluminum piston sealing on a delrin face and it does not seal completely until it reaches 200 psi or so.

I thought high pressures (relatively) might be needed for a good seal. I'm impressed by the 100 PSI sealing, Gippeto; that's lower than I expected possible. The undercut idea is genius; less surface area on the actual sealing face, but more surface area to present to the pressure chamber, right?Not quite sure how to interpret your schematic, though. Which lines are which part? Or is it all one part (a delrin block attached to the valve stem)?

jackssmirkingrevenge wrote: aluminum piston sealing on a delrin face and it does not seal completely until it reaches 200 psi or so.

How does that affect re-sealing after firing, JSR? Does the 'slam' of the piston into the delrin face as it closes allow it to compress the delrin and seal properly? It seems like would be hard on the delrin. Or is the stuff tougher than that? I confess, I've not had a chance to use any, yet.

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“Whenever you find yourself on the side of the majority, it is time to pause and reflect.”Mark Twain